Outcome assessment. Any individual with sinus arrhythmia present in over 50% of ECGs during the two study visits will be dropped from analysis. ECGs with premature ventricular or atrial beats will be dropped from analysis (these are very uncommon in healthy volunteers). The QTc using Fridericia's heart rate correction (QTc = QT/3√RR) will be taken as the average of all eligible ECGs from each time point. The ΔQTc will be calculated as the difference in QTc from baseline (after study drug/placebo administration) for each time point. From the ΔQTc, the difference between the post-moxifloxacin and post-placebo ΔQTc will then be calculated at each time point (ΔΔQTc) as well. The mean ΔΔQTc from the 180-300 minute time points (which from our pilot work and published reports is expected to be 10 msec) will then be compared between the two genotype groups (top and bottom and quintile) using an unpaired t-test. We estimate that 40 people in each group will be needed to have adequate power to detect a clinically meaningful (6.3 msec) difference in QT-prolongation between the two groups based on our pilot data (Table 2). An increase of 6 msec after exposure to a drug compared to placebo is the threshold at which the FDA raises concern for the potential of a drug to cause torsade de pointes and is thus clinically significant.